1. Field of the Invention
This invention relates to a communication control system in a communication system which connects a plurality of communication stations on a communication channel.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional communication control system shown in, for example, the book entitled "A GUIDE TO DATA COMMUNICATION SYSTEM OF ILLUSTRATED COMPUTER SERIES" (Written by IWAO HOSAKA, published by OHM CO., Ltd. on Jan. 30, 1980), in which numeral 1 denotes a master communication station which supervises the communication system concerned, numerals 2 denote slave communication stations #1 through #n, and numeral 3 denotes a communication channel which connects the master communication station 1 with the slave communication stations 2 and connects the slave stations with one another.
Next, the operation of the communication system will be described. After the communication system has been started, the master communication station 1 has the leadership and executes communication control of the communication system concerned. In other words, after the master station 1 has started, it produces data addressed to the #1 slave communication station 2 and sends out the data onto the communication channel 3. The data are received at the #1 slave communication station 2 through the communication channel 3. After the completion of the reception of the data, the #1 slave communication station 2 concerned produces data addressed to the master communication station 1 and sends out the data onto the communication channel 3. The master communication station 1 receives the data. After the completion of the reception of the data, the master communication station 1 produces data addressed to the #2 slave communication station 2 and sends out the data onto the communication channel 3. Thereafter, the above-mentioned communication control is executed in order in the same way as above. The following communication such as the master communication 1 .fwdarw. the #1 slave communication station 2 .fwdarw. the master communication station 1 .fwdarw. the #2 slave communication 2 .fwdarw. the master communication station 1 .fwdarw. the #3 slave communication 2 .fwdarw. the master communication station 1 .fwdarw. . . . .fwdarw. the master communication station 1 .fwdarw. the #n slave communication station 2 .fwdarw. the master communication 1 .fwdarw. the #1 slave communication station 2 .fwdarw. is executed.
Since the conventional communication control system is constituted as described above, when any trouble happens in the master communication station 1 which supervises the communication system concerned, e.g. any electrical or mechanical difficulty preventing the station from effectively receiving and transmitting data, the influence extends to the whole of the communication system. That is, there is a problem that any trouble in only one communication station, e.g. the master communication station 17 makes the whole of the communication system break down.